The objective of this proposal is to investigate the biological role of the bvg sensory transduction system which regulates expression of virulence factors in members of the genus Bordetella. In Bpertussis, the bvg products are required for expression of adhesins, toxins, and other virulence associated products. In addition to positive control, bvg also negatively regulates several Bpertussis loci, as weU as the phenotypes of motility and flagellation in B.bronchiseptica. Although the function of the bvg regulatory apparatus is to sense and respond to the environrnent, we have no indication of the role of this signal transduction system duzing infection or disease. Our experiments wiU test the hypothesis that sensory transduction occurs in vivo, and that the ability to respond to the envirownent is of central importance during the Bordetella infectious cycle. This suggestion predicts that alteration or elimination of the sensory i-esponse wffl result in notable differences in the outcome of infection. The bvg systems encoded by Bpertussis and B.bronchiseptica are nearly identical. Although Bpertussis has adapted exclusively to the human host, B.bronchiseptica naturaHy infects a variety of laboratory animals. We plan to exploit this and use a recently developed B.bronchiseptica guinea pig infection model to study sensory transduction in the context of a natuml host-parasite interaction. Mutadons at the B.bronchiseptica bvg locus that specificauy affect the ability to respond to the environment will be isolated and characterized. The ability of sensory transduction mutants to infect, persist, and cause disease will be compared with wild gW snffis. We will also exaniine the in vivo role of several loci that are negatively controlled by bvg, and develop techniques for direct" examinadon of bacterial gene expr-ession during infection. B.bronchiseptica and Bpertussis are closely r-elated organisms. We are hopeful that our analysis of B.bronchiseptica vindence gene regulation during infection of a natural host will have implications for pertussis vaccine efforts, and highlight a crifical aspect of bacterial-host interactions.